Molten carbonate fuel cell stacks utilize a melted carbonate electrolyte which is contained in an inert porous matrix plate. Preferably, the stacks will also include excess molten electrolyte which will be contained in electrolyte reservoir plates that also serve as the electrodes. The excess electrolyte will migrate into the matrix plate as needed. Since the carbonate electrolyte in these power plants is a solid at ambient temperatures, the problem is how to load such electrolytes into the matrix and reservoir plates in the stack. One procedure for forming such loaded plates is to form a green tape plate from lithium aluminate matrix particles, and carbonate electrolyte particles which are all held together by a binder. These electrolyte-matrix tapes are placed between the electrodes during assembly of the stack, and the binder is burned out of the tape during stack heat-up, and the carbonate particles are melted in situ in the interstices of the lithium aluminate matrix.
The aforesaid procedure for forming loaded matrix or reservoir plates causes the plate particles to be separated from each other due to the presence of the carbonate particles in the green tape. The resultant lithium aluminate matrix will thus have larger pores than desired, which causes the stack to be dimensionally unstable, and the matrix layers in the stack may collapse to some extent. The cumulative result of matrix collapse of the matrices in a multi-cell stack can cause the operative portions of the stack to slide against the manifold seals to damage the latter.
One manner of avoiding the aforesaid problems which arise has been to place dry powdery carbonate on the electrode plates; preheat the plates prior to forming the stack so as to melt the carbonate powder. Once the carbonate powder melts, it will seep into the electrode/ER plate interstices. This approach has proven feasible for use in stacks which have sufficiently thick electrode/ER plates so as to accommodate a large enough amount of the carbonate powder to ensure that after the electrolyte has filled the matrix plate, a satisfactory amount of the melted electrolyte will remain in the electrode/ER plates to provide sufficient ER electrolyte to replenish electrolyte lost from the matrix plates over an extended period of time to prolong stack life. This type of procedure does not adversely affect stack integrity because the matrix and ER electrode plates are preformed. The aforesaid solution to the problem of electrolyte loading is not effective unless the electrode plates are relatively thick. When relatively thin electrode/ER plates are needed for enhanced stack performance, the preloading of the electrode plate with carbonate electrolyte is ineffective because of the lack of sufficient electrolyte capacity due to the thinness of the electrode.